1. Field of the Invention
The present invention relates to a magnetic recording medium for use as a video tape, audio tape, memory tape, etc.
The features of the present invention are as follows.
(1) The backing layer has turned white or light color, and the writing property or marking property is excellent as compared with a conventional black backing layer.
(2) Pinholes or drop-out in coating of a magnetizable layer can be detected with ease in the production step.
2. Description of the Prior Art
In general, a magnetic recording medium comprises a base having on the one side thereof a magnetizable layer and, on the opposite side, a backing layer. As the backing layer, graphite, carbon black, etc. are often used, depending upon the use of the tape.
A magnetic recording medium having such a structure can be used with no problems under usual conditions. However, there is room for improvement in such a tape in electrostatic adsorption of dust, unevenness at the edge surface of the wound tape and the like.
As a means to improve these defects, it has been known to provide a backing layer having a low electric resistance and a rough surface.
In general, the backing layer used at present for the above-described purposes (i.e., to prevent the electrostatic adsorption of dust and unevenness at the edge surface of the wound tape by reducing electric resistance and rendering the surface rough) in the magnetic recording medium having a structure as described mainly comprises a mixture of carbon black and an organic binder. Such backing layer is necessarily of a black color, which makes marking thereon and the detection of the contents and the position of marks difficult.
In order to solve the problems, it has been suggested to improve a writing ink, but, at the present a satisfactory writing ink has not yet been invented.
In the case of producing a magnetic tape, there can be employed various coating methods such as doctor coating, reverse coating, gravure coating, etc. However, none of these coating methods enables one to completely remove pinholes or the similar drop-out effect encountered in coating. Therefore, it is important to be able to detect pinholes or drop-out in the coating during the production step. In conventional methods as above, the detection thereof by a method utilizing transmitted light is almost impossible due to the backing layer being black. Although there can be employed other detecting methods such as a light reflection method and a magnetic head method, the former has the defect that operation is unstable and the latter has the defect that small pinholes are difficult to detect and, since it is of the contact type, the magnetic tape being inspected is liable to be flawed.
If a product having pinholes or drop-out resulting from coating was sold due to an error in detection, serious problems to the consumer or users would result since good reproduction of signals is impossible.
Therefore, the detection of pin-holes and drop-out is an extremely important matter for magnetic tape manufacturers.